Expression patterns of mRNAs for α-fetoprotein and albumin in the developing rat: the ontogenesis of hepatocyte heterogeneity

Summary In developing and normal adult rat liver the expression patterns of the mRNAs for -fetoprotein (AFP) and albumin (ALB) were analysed byin situ hybridization using specific³⁵S-labelled complementary DNA probes. In the developing liver AFP and ALB mRNA are found from embryonic day (ED) 11 and 12, respectively, onward. At ED 20 the first signs of a zonal distribution of these mRNAs across the liver lobule can be observed, AFP mRNA concentration being higher in the pericentral area and ALB mRNA concentration higher in the periportal area. This distribution pattern of reciprocal, overlapping gradients of mRNA can be clearly recognized in the neonatal period. In the adult liver AFP mRNA can no longer be detected and similar to the neonatal situation, ALB mRNA is expressed across the entire porto-central distance decreasing in concentration going from the portal to the central area.Transient extra-hepatic expression of AFP mRNA is found in the embryonic heart and in the epithelial lining of intestine and lung furthermore, AFP and ALB mRNA are found to be transiently expressed in the developing renal tubules. Similar expression patterns have been observed for other liver-characteristic mRNAs (Moormanet al., 1990), suggesting that common regulatory factors are operative during development.     

Expression in Escherichia coli and purification of a translocation-competent precursor of the chloroplast protein ferredoxin

The precursor of the chloroplast protein ferredoxin from Silene pratensis was expressed in Escherichia coli. When a low copy number plasmid was used, the preferredoxin level was low, and the protein was soluble. The expression level was increased by using a high copy number plasmid. In protease-deficient cells transformed with the latter plasmid, the preferredoxin accumulated up to 1% of total protein, and it was found in insoluble aggregates. These aggregates were dissolved in 4 M urea, and the protein was purified to homogeneity. Amino-terminal sequencing confirmed the amino acid sequence as deduced from the copy DNA. However, the first methionine residue of the expected sequence was absent in E. coli. The purified precursor was readily imported by isolated chloroplasts and processed to the mature size.     

Nucleo-cytoplasmic interactions causing partial female sterility in the spider mite Tetranychus urticae Koch (Acari: Tetranychidae)

A case of non-reciprocal hybrid infertility between strains of the spider mite Tetranychus urticae Koch is described. Evidence is presented that the infertility results from an interaction between a chromosomal and a cytoplasmic factor. The presence or absence of the cytoplasmic factor seems to be controlled also by chromosomal genes.     

On the survival of populations in a heterogeneous and variable environment

Summary The survival time of small and isolated populations will often be relatively low, by which the survival of species living in such a way will depend on powers of dispersal sufficiently high to result in a rate of population foundings that about compensates the rate of population extinctions. The survival time of composite populations uninterruptedly inhabiting large and heterogeneous areas, highly depends on the extent to which the numbers fluctuate unequally in the different subpopulations. The importance of this spreading of the risk of extinction over differently fluctuating subpopulations is demonstrated by comparing over 19 years the fluctuation patterns of the composite populations of two carabid species, Pterostichus versicolor with unequally fluctuating subpopulations, and Calathus melanocephalus with subpopulations fluctuating in parallel, both uninterruptedly occupying the same large heath area. The conclusions from the field data are checked by simulating the fluctuation patterns of these populations, and thus directly estimating survival times. It thus appeared that the former species can be expected to survive more than ten times better than the latter (other things staying the same). These simulations could also be used to study the possible influence of various density restricting processes in populations already fluctuating according to some pattern. As could be expected, the survival time of a population, which shows a tendency towards an upward trend in numbers, will be favoured by some kind of density restriction, but the degree to which these restrictions are density-dependent appeared to be immaterial. Density reductions that are about adequate on the average need even not occur at high densities only, if only the chance of occurrence at very low densities is low. The density-level at which a population is generally fluctuating appeared to be less important for survival than the fluctuation pattern itself, except for very low density levels, of course. The different ways in which deterministic and stochastic processes may interact and thus determine the fluctuations of population numbers are discussed. It is concluded that some stochastic processes will operate everywhere and will thus necessarily result in density fluctuations; such an omnipresence is much less imperative, however, for density-dependent processes, by which population models should primarily be stochastic models. However, if density-dependent processes are added to model populations, that are already fluctuating stochastically the effects are taken up into the general, stochastic fluctuation pattern, without altering it fundamentally.Communication No. 228 of the Biological Station WijsterDedicated to Professor Michael Evenari     

Glycosylation in vitro of an asparagine sequon catalysed by preparations of yeast cell membranes.

Preparations of yeast cell membranes can catalyse in vitro the N-acetyl-beta-D-glucosaminylation of the asparagine sequon at residues 34--36 of bovine pancreatic ribonuclease A. The relevant glycopeptides were isolated from tryptic hydrolysates of the glycosylated ribonuclease and analysed. The donor used was UDP-N-acetyl-D-glucosamine, although the mechanism of the transfer is unknown. Mn2+ ions at concentrations of 25 mM double the activity of the enzymic transfer.     

Further studies on the formation of cardiolipin and phosphatidylglycerol in rat liver mitochondria. Effect of divalent cations and the fatty acid composition of CDP-diglyceride.

The divalent cation requirement for mitochondrial cardiolipin biosynthesis has been further investigated. The relative order of divalent cation activity was Co-2+ greater than Mn-2+ greater than Mg-2+. Cardiolipin was not formed in the incubations with Zn-2+, Fe-2+, Cu-2+, Hg-2+, and Ca-2+. Cardiolipin synthesis in the presence of optimal cincentration of Co-2+ was inhibited by Ca-2+. A series of CDP-diglycerides was synthesized having differences in fatty acid chain lenth and degree of unsaturation. These compounds were tested in mitochondrial cardiolipin and phosphatidylglycerol synthesis. Although there were some minor differences between phosphatidylglycerol and cardiolipin synthesis, in general, saturated shorter chain CDP-diglycerides (dilauroyl and dimyristoyl) were better substrates than the longer chain dipalmitoyl and distearoyl homologues. Introduction of double bonds into distearoyl CDP-diglyceride resulted in more rapid rates of synthesis (e.g. dioleoyl and dilinoleoyl CDP-diglyceride). Significance of the results is dicussed with regard to possible mechanisms of linoleic acid incorporation into rat liver cardiolipin.     

Localization of acid phosphatase in protoplasts from Saccharomyces cerevisiae.

The localization of acid phosphatase (EC 3.1.3.2) in secreting protoplasts prepared from Saccharomyces cerevisiae is reported for the first time. Using a Gomori technique we were able to show acid phosphatase at those organelles in the protoplasts which are generally involved in the processes of biosynthesis and secretion of glycoproteins in eukaryotic cells.